Kiyohiro Ito

Transfer Matrix Analysis for Curved Beam Structure

The curved beam structure such as pipe system has been widely used in industrial plants or power stations. In this study, the reduction technique of stiffness matrix, which is refered to “transfer matrix method (TM)“, is developed to solve effectively the problem. For achieving the purpose, the transfer matrix Fk to transfer deformation, rotation, force and moment from node i to node i+1, which are named for both edges in k-th beam element, is formulated. The global transfer matrix is then constructed by multiplying as R(θk+1,k)·Fk···R(θ2,1)·F1···R(θk+1,k) is the coordinate rotation matrix. The efficiency and simplicity of this method is demonstrated by solving the problem of a curved pipe line with elbow which is subjected to external forces and displacements. The results are compared with those obtained by FEM.

Comprehensive Numerical Simulation of Stress and Damage Fields under Thermo-Mechanical Loading for TBC-Coated Ni-Based Superalloy

A finite element analysis code was developed to accurately predict stress and damage fields in thermal barrier coatings (TBCs) systems subjected to thermo-mechanical loadings. An inelastic constitutive equation for TBCs, and a Chaboche-type viscoplastic constitutive equation for Ni-based super alloys (IN738LC) were employed to simulate high temperature creep and cyclic deformation. Simulations of the TBC/IN738LC system subjected to two types of loading, namely, a triangle-wave loading and a GT-operation loading, were performed using the developed analysis code. The results confirmed that the stress and damage fields in the TBC/IN738LC system could be simulated accurately, and provided us with credible results regarding the crack occurrence. Additionally, the analysis under the GT-operation loading conditions revealed that a peak stress generated during the start-up operation would lead to delamination of the TBC, while a peak stress at the shut-down would lead to cracking in the substrate.

Electrochemical Migration of Copper Caused by Volcanic Ash Deposited on Printed Circuit Boards

When volcanic ash is suffiently fine, that it can pass through a filter and be deposited on a printed circuit board, electrochemical migration (ECM) is expected to be strongly affected by the deposited volcanic ash. In this study, to better understand the influence of volcanic ash on ECM, a water drop (WD) test is performed on two biased Cu electrodes using distilled water droplets containing five samples of volcanic ash from eruptions of different volcanos. From the results, it is seen that all of the volcanic ash droplets exhibited electrical conductivity. The ECM process was accelerated by three of the volcanic ash samples and was negligibly affected by the other two. In addition, both the acceleration and deceleration of the ECM were strongly affected by the content of volcanic ash from Mt. Shinmoe. The WD tests, performed using a commercial SiO2 powder, revealed that the growth of Cu dendrite is physically interrupted by the particles of volcanic ash. Furthermore, the WD tests, performed using the supernatant liquids of each volcanic ash and H2SO4 solutions, revealed electrical conductivity, and that the acceleration of ECM results from water-soluble components, primarily the SO42− ions dissolved from the volcanic ash. Consequently, the acceleration or deceleration of ECM is determined by the balance between the acceleration by water-soluble components and interruption by the particles.